trans help please!

ChrisM · December 3rd, 2008, 11:56 AM

Hello all,
I have a '73 delta 88 with the 350 engine and i think the th400 trans. My problem is that the trans is shifting out of first way late. I don't have a tach in the car, but the rpm's sound way too high. The trans shifts out of the other gears in what seems like the correct time, but first is a problem. I should also mention that it seems to shift a little earlier after the car is warm. My only quantifyable info to pass along is that when cold the trans shifts out of first at around 30 miles per hour, and when warm it shifts out of first at around 25 miles per hour.

Any ideas? What should I check? Is there possible some sort of vacuum line or something that goes from engine to trans that I should check? I really don't know anything about trans, so any help would be great.

Thank you all in advance,
Chris

Cutlass69S · December 3rd, 2008, 01:46 PM

Chris, there is a vacuum modulator on the passenger side of the trans, it is a small canister. You should check/replace it, first check the vacuum, it should be approx. 15 to 20 . If you have a steady vacuum at the modulator, then it is possible your modulator has a pin hole in the diaphragm or the actual modulator valve is sticking. Did you put a new modulator in it, if so, it is adjustable and may simply need an adjustment. The adjustment is located inside the vacuum tube of the modulator. As long as the trans isn't slipping, you should have a fairly simple and inexpensive problem. One other thing to notice is that the governor opposite of the modulator side of the trans should shift you at 22 miles per hour. The governor could be dirty, think about draining the trans and installing a new filter and fluid. gl

69 Cutlass Holiday Coupe
66 Chevy street rod truck
71 Nova 2 door hard top
02 Silverado
91 21' Stingray
85 Kawasaki
84 Kawasaki
02 Yamaha
92 Huffy.....etc.

ChrisM · December 7th, 2008, 11:24 PM

thanks for the comments Cutlass69S. I have been crazy busy lately, so I was hoping to wait a while before I dig into this, but the trans is shifting even a few miles per hour later now, so I will give your suggestions a try as soon as I can. One question, what do you mean by the trans slipping?

Thanks,
Chris

ChrisM · December 12th, 2008, 01:31 PM

THANK YOU CUTLASS69S!!!! That is exactly what the problem was. I got underneath the car to take a look at vacuum modulator, and the vacuum hose connected to the mudulator had a huge split in it. I replaced the hose with one I had in the garage, and problem fixed! Once again this site has given me the answer to my problem. Thanks !!!!

December 3rd, 2008, 11:56 AM	#1 (permalink)
ChrisM Registered User Join Date: Oct 2007 Location: Southern California Posts: 73	trans help please! Hello all, I have a '73 delta 88 with the 350 engine and i think the th400 trans. My problem is that the trans is shifting out of first way late. I don't have a tach in the car, but the rpm's sound way too high. The trans shifts out of the other gears in what seems like the correct time, but first is a problem. I should also mention that it seems to shift a little earlier after the car is warm. My only quantifyable info to pass along is that when cold the trans shifts out of first at around 30 miles per hour, and when warm it shifts out of first at around 25 miles per hour. Any ideas? What should I check? Is there possible some sort of vacuum line or something that goes from engine to trans that I should check? I really don't know anything about trans, so any help would be great. Thank you all in advance, Chris

December 3rd, 2008, 01:46 PM	#2 (permalink)
Cutlass69S Member Join Date: Aug 2008 Posts: 35	Chris, there is a vacuum modulator on the passenger side of the trans, it is a small canister. You should check/replace it, first check the vacuum, it should be approx. 15 to 20 . If you have a steady vacuum at the modulator, then it is possible your modulator has a pin hole in the diaphragm or the actual modulator valve is sticking. Did you put a new modulator in it, if so, it is adjustable and may simply need an adjustment. The adjustment is located inside the vacuum tube of the modulator. As long as the trans isn't slipping, you should have a fairly simple and inexpensive problem. One other thing to notice is that the governor opposite of the modulator side of the trans should shift you at 22 miles per hour. The governor could be dirty, think about draining the trans and installing a new filter and fluid. gl 69 Cutlass Holiday Coupe 66 Chevy street rod truck 71 Nova 2 door hard top 02 Silverado 91 21' Stingray 85 Kawasaki 84 Kawasaki 02 Yamaha 92 Huffy.....etc. Last edited by Cutlass69S; December 3rd, 2008 at 01:48 PM..

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December 7th, 2008, 11:24 PM	#3 (permalink)
ChrisM Registered User Join Date: Oct 2007 Location: Southern California Posts: 73	thanks for the comments Cutlass69S. I have been crazy busy lately, so I was hoping to wait a while before I dig into this, but the trans is shifting even a few miles per hour later now, so I will give your suggestions a try as soon as I can. One question, what do you mean by the trans slipping? Thanks, Chris

December 12th, 2008, 01:31 PM	#4 (permalink)
ChrisM Registered User Join Date: Oct 2007 Location: Southern California Posts: 73	THANK YOU CUTLASS69S!!!! That is exactly what the problem was. I got underneath the car to take a look at vacuum modulator, and the vacuum hose connected to the mudulator had a huge split in it. I replaced the hose with one I had in the garage, and problem fixed! Once again this site has given me the answer to my problem. Thanks !!!!